The present invention relates to the field of corrosion testing of zirconium and zirconium base alloys and is most particularly concerned with the corrosion testing of zirconium alloy weldments.
Zirconium alloys are commonly used in commercial pressurized water and boiling water nuclear reactors for structural elements such as fuel rod channels and grids, and as heat transfer elements such as tubular fuel cladding. One of the most common methods of joining one zirconium alloy member to another to form the aforementioned elements is by welding.
Zirconium and its alloys are well known to be highly reactive materials at high temperatures; that is, they readily, and rapidly, combine with oxygen and nitrogen in the atmosphere. It is known that the contamination of zirconium alloys with these elements can adversely affect the aqueous corrosion resistance and/or mechanical properties of the alloy. It is therefore common practice in the welding of zirconium alloy nuclear components to perform all welding in an inert atmosphere such as in a vacuum, or in a helium or argon atmosphere. For example, the girth welds joining Zircaloy-4 end plugs to the ends of Zircaloy-4 fuel cladding are typically formed by Tungsten Inert Gas (TIG) welding in a helium-filled chamber. To assure that air is not leaking into the welding chamber and contaminating the weldment, weldment samples are periodically subjected to a three-day 360.degree. C. (680.degree. F.) water corrosion test (ASTM Test No. G2).
While this test is very successful in detecting weldment samples having harmful impurity levels, especially nitrogen, it is time consuming. It takes three, to as long as seven days, to obtain test results. Due to this long turnaround time, the three-day water test is of little value as a process control test. Also, the storage space required for welded product awaiting acceptable test results is costly and increases inventory control problems. It is therefore desirable to develop a test which is as capable as the three-day water test in detecting weldments with deleterious impurity levels, but which is significantly more rapid.